The 是…的 (shì…de) construction vs 了 (le) in Chinese grammar

Both the 是…的 (shì…de) construction and 了 (le) can both be used to talk about past events in Mandarin Chinese grammar. Here's how to use the two constructions correctly, as they are different.

是…的 (shì…de): focus on the circumstances

A quick recap of the 是…的 (shì…de) construction.

是…的 is used to talk about events that happened in the past:


Zhè jiā gōngsī shì èr líng yī bā nián jiànlì de.

The company was founded in 2018.

是…的 can also emphasise some information in a sentence (that describes a past event):


Bāoguǒ shì zuótiān sòng dào de.

The parcel was delivered yesterday.


Tā shì qí chē qù chéngshì lǐ de.

She went into town by bike.

The 是…的 construction describes past events, and can also emphasise particular details of a sentence such as time, manner or place.

Because 是…的 emphasises the circumstances of past events, it's useful for describing how, where or when something happened.

An example of using 是…的 to describe how something happened:


Wǒ shì gēn wǒ de péngyou men yīqǐ qù de.

I went with my friends.

⇒ It was with my friends that I went.

An example of using 是…的 to describe where something happened:


Zhè liàng zìxíngchē shì wǒ zài wǎng shàng mǎi de.

I bought this bike online.

⇒ It was online that I bought this bike.

An example of using 是…的 to describe when something happened:


Tā shì zuótiān wǎnshang dào de.

He arrived last night.

⇒ It was last night that he arrived.

The most important point is that 是…的 is suitable for describing the circumstances or manner of things in the past.

了 (le): focus on completion

Unlike 是…的, 了 (le) is not necessarily about the past. See this 了 (le) grammar summary for more details.

了 has many uses, one of which is about marking completeness of actions. 了 is commonly misunderstood as being about the past tense, but 了 is not about the past tense (Chinese grammar does not really have tenses).

Some examples using 了 that show how it is about completeness of an action, or a new state:


Wǒ zuótiān qù le.

I went yesterday.

⇒ I did go yesterday.


Wǒ lái le.

On my way!


Tā yào shēngqì le.

He's going to get angry.

Other than not necessarily being about the past, 了 is also different to 是…的 in that it cannot be used to describe the circumstances of an action, only the completeness.

Comparing 是…的 and 了

Compare these sentences that are the same other than the use of 是…的 or 了:


Wǒ zuótiān mǎi le miànbāo.

I bought bread yesterday.

⇒ I did buy bread yesterday.


Miànbāo shì zuótiān mǎi de.

The bread was bought yesterday.

Both describe an event in the past. The 了 sentence only indicates that the action was completed in that timeframe, whereas the 是…的 sentence emphasises the circumstances (the time it happened).

You can also see the difference if we make those sentences into questions:


Nǐ zuótiān mǎi le miànbāo ma?

Did you buy bread yesterday?

⇒ Did you buy bread [yesterday]? [most interested in whether bread was bought or not, less so in when it happened.]


Miànbāo shì zuó mǎi de ma?

Did you buy the bread yesterday?

⇒ Was it yesterday that the bread was bought? [and not some other day]

The difference seems subtle, but pay attention to the re-phrasings that highlight where the emphasis is.

With “你昨天买了面包吗?”, it seems that buying bread might be a regular occurrence, or at least that the asker expected you to have bought bread yesterday. They are primarily asking whether or not this action was completed at all, and the time is just a bit of context for the question.

With “面包是昨买的吗?”, the fact the bread was purchased is already an established fact. The asker wants to know specifically whether it happened yesterday and not some other day. Perhaps the asker wants to know how fresh the bread is, so they use 是…的 to focus on the circumstances of the action, in this case the time.

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